There is no admission that the background art disclosed in this section legally constitutes prior art.
Conditions related to back pain account for more hospitalizations than any other musculoskeletal condition. The back is the body part most often involved in work-related disabilities. Back pain is the most prevalent medical disorder in industrialized societies. More than 75% of the United States population will be affected by low back pain over the course of their lifetime. According to the statistics from the National Institutes of Health, back pain is the second most common medical condition for which people seek treatment, accounting for more than 50 million physician office visits annually. Low back pain is the leading cause of disability in people younger than age 50.
In order to alleviate back pain, many people undergo surgical intervention. Implanted instrumentation is used in many types of spinal surgeries to help join vertebrae together and restore stability. Additionally, implants such as plates, rods, and screws help correct deformity and bridge spaces created by the removal of damaged spinal elements. Bone cement is desired in clinical situations to enable proper fixation of the implants. Bone cement is also used in a wide variety of other medical and dental applications, such as in the repair of cranio-maxillofacial defects, tooth fillings, or spinal fusions.
The bone cements commonly used are poly methyl methacrylate (PMMA) cements. Bone cements made from PMMA have several disadvantages. Namely, methacrylates and methacrylic acid are known irritants to living tissue. PMMA-based cements can generate free radicals in vivo, which can damage surrounding tissue. PMMA-based cements are also not biodegradable, and the polymerization reaction involving PMMA is highly exothermic, possibly causing damage to surrounding tissue when cured.
Another problem with many conventional bone cement formulations is the necessity of mixing and storing two or more solid powder ingredients, which reduces their batch-to-batch reproducibility and shelf life. Homogeneous mixing of two solids is not an easy task. Optimal cements should be able to set in a liquid medium during the normal setting time without being washed away. This is important for injectability and cohesiveness. Both of these issues can be enhanced by incorporating a polymer in the setting solution. However, cement compositions containing polymers with two solid ingredients still have poor injectability because homogeneous mixing of two solid ingredients is not easy.
Some possible alternatives to PMMA-based cements are cements made from various alkaline earth phosphates. These include calcium phosphate cements, magnesium phosphate cements, and strontium phosphate cements. Of all alkaline earth phosphates, Ca—P cements, or CPCs, are the most common. CPCs are based on different compounds within the CaO—P2O5 (Ca—P) binary system. These compounds include Ca-hydroxyapatite, Ca10(PO4)6(OH)2 or simply hydroxyapatite, which is most well known due to its similarity to natural bone mineral. Other compounds in the Ca—P binary system include tetracalcium phosphate (TTCP, Ca4(PO4)2O), tricalcium phosphate [α-TCP, α-Ca2(PO4)2 and β-TCP, β-Ca3(PO4)2], dicalcium phosphate anhydrous (DCPA, monetite, CaHPO4), di-calcium phosphate dehydrate (DCPD, brushite, CaHPO4.2H2O), and octacalcium phosphate (OCP, Ca8H2(PO4)6.5H2O). CPCs offer several advantages over PMMA-based cements, such as greater malleability, allowing the cement to better adapt to a defect's site and shape. CPCs also offer better biocompatibility, bioactivity, osteoconductivity, and bioresorbability.
Mg—P cements (MPCs) in the market are mainly based on the composition of MgNH4PO4, formed via reaction between acid part (ammonia salts) and base part (MgO or Mg(OH)2), resulting in exothermic phenomena. However, the release of ammonia during setting and degradation of MPCs compromises the biocompatibility of the cements. Sr—P cements (SPCs) are Ca—P or Mg—P cements doped with strontium. Strontium can promote cell growth and provides radio opacity.
It would be desirable to formulate bone cement compositions that are easily made and possess improved strength, mechanical properties, and bioactivity. It would be further desirable if the properties of such bone cements allow them to be readily used in the surgical theater.